Placental transport and fetal metabolism of vitamin A are responsive to low and high maternal vitamin A intakes. In addition, maternal vitamin A intake alters colostrum and milk levels of vitamin A, perhaps rendering the neonate susceptible to hypo or hypervitaminosis A. Common nutritional disorders in pregnancy and neonatal life include deficiencies of vitamin A and protein. Abnormal metabolism of retinol has been demonstrated with dietary deficiencies of protein and, although the syndrome clinically is one of vitamin A deficiency, best therapeutic responses are seen with supplements of protein as well as vitamin A. Prevention of vitamin A related disorders in children will necessarily involve further understanding of the roles of vitamin A and protein in retinol metabolism. We propose a study of the effect of varied vitamin A and protein intakes on retinol homeostasis in fetal and neonatal life. In the first experiment, neonatal lambs from ewes fed daily 0, 120, 1,200 or 12,000 Mug retinol/kg body weight will be fed colostrum containing labelled vitamin A obtained from ewes fed the 4 vitamin A levels. Vitamin A transport into colostrum and milk and neonatal absorption and metabolism of vitamin A will be examined. In the second experiment, pregnant sheep fed diets of 6, 10 or 14% crude protein will be administered 3H-retinol. Placental transport will be determined by blood sampling the ewe and her chronically catheterized fetal lamb for 30 to 40 days (until parturition). In our third experiment, neonatal lambs from ewes fed diets containing 6, 10 or 14% crude protein will be fed colostrum containing labelled vitamin A obtained from ewes fed the 3 protein levels. In both experiments, fluids and tissues will be analysed for labelled and non-labelled vitamin A fractions and biochemical criteria. Our proposed study would add important information crucial to our understanding of vitamin A-related disorders and provide data on vitamin A and protein intakes for optimal vitamin A metabolism in pregnant, fetal and neonatal life.